Shortly after Trump gave Mattis full authority to set troop levels, National Security Adviser Lt. Gen. H.R. McMaster sent a memo around the White House saying that the Pentagon chief had to check with them in order to deploy more than 3,900 troops, the Wall Street Journal reported.

The Associated Press reported in June that the Pentagon would be sending nearly 4,000 more US troops to Afghanistan to train local forces fighting the Taliban and ISIS, but the Defense Department quickly denied the report.

The Trump administration, which is still considering sending 2,500 to 5,000 more troops to Afghanistan, is reportedly split on what to do about America’s 16-year long war — the longest in US history.

Mattis and Lt. Gen. HR McMaster both support a troop surge in Afghanistan. But Trump’s chief strategist, Stephen Bannon, sees this move as akin to nation-building, The New York Times reported in May. Trump’s son-in-law and senior adviser, Jared Kushner, is also reportedly critical of US policy in Afghanistan.